This invention pertains generally to the field of liquid ink jet printer systems, and more particularly to an apparatus and method for drying receiver media in an ink jet printing system.
For photographic-quality ink jet printing, it is desirable to deposit a number of droplets at each location in the paper, so that a sufficiently high gray-scale is obtained. In prior art scanning-type print heads, this is accomplished by reciprocating the print head over the same location on the receiver a number of times and depositing ink droplets as required by the images to be printed. Since it takes several hundred milliseconds (msec) for the printhead to return to a previous location, any ink droplets deposited at that location will have adequate time to diffuse many microns into the paper receiver. Ink droplets that are subsequently deposited at that location can then be deposited on top of the previous droplets without producing visible artifacts.
In a high-speed, high-resolution ink jet printing system, such as page-width ink jet printing systems, the relatively long time of 1 to 100 msec or more required for the ink to diffuse into the paper receiver (away from the receiver surface) produces visible artifacts. For example, if an x-y (Cartesian coordinates) array of droplets are deposited on the receiver at a predetermined printhead resolution, the separate droplets coalesce into a larger droplet that results in an uneven distribution of dye and thus a possible undesirable image artifact. This is illustrated in FIGS. 1A and 1B, where FIG. 1A shows a plurality of ink droplets 10 deposited on a surface 20 of a paper receiver 30, and FIG. 1B shows droplets 10 having coalesced into a xe2x80x9ccoalescedxe2x80x9d droplet 40. FIG. 1C shows a desired dye diffusion pattern into the paper receiver, and FIG. 1D shows an undesirable non-uniform dye distribution due to droplet coalescence.
The situation is worse in multicolor closely-spaced page-width printhead systems, wherein an undesirable mixing of different color dyes can take place due to coalescence.
Droplet coalescence occurs because of the slow rate of penetration of ink into the paper receiver. This rate is at best approximately 30 xcexcm in 100 msec. To avoid coalescence, this penetration rate should be increased to approximately 30 xcexcm in 30 xcexcsec, which is approximately 1.0 xcexcm/xcexcsec.
The present invention pertains to an apparatus and method for drying a receiver media in an ink jet printer. By way of example and not of limitation, the apparatus of the present invention generally comprises a means for creating a pressure differential between the upper surface and the lower surface of the receiver media, wherein the pressure at the lower surface of the receiver media is lower than the pressure at the upper surface of the media. The pressure differential-creating means may include a vacuum pump adapted to generate a vacuum at the lower surface of the receiver media or an air pump adapted to pass air currents across the lower surface of the receiver media to cause a Bernoulli effect. Ink carrier fluid is recaptured and may be recycled.
By way of example and not of limitation, the method generally comprises the steps of depositing ink droplets onto the upper surface of the receiver media; and creating a pressure differential between the upper surface and the lower surface of the receiver media, whereby fluid contained in ink droplets is drawn through the receiver media from the upper surface to the lower surface.
The pressure differential between the lower surface and the upper surface of the receiver media eliminates ink droplet coalescence by increasing the flow rate of the ink fluid through the receiver media. The elimination and/or reduction of ink drop coalescence provides for a more uniform dye distribution on the receiver media, and hence, enhanced image quality from the ink jet printer.